Creatine and creatinine metabolism in uraemia.

Measurements of serum creatinine to monitor the progression of chronic renal failure may be misleading and influenced by factors other than GFR. Creatinine is produced by the degradation of creatine which is stored in muscle. The effect of biochemical changes observed in uraemia on the transport of [1-14C]creatine were examined in a cultured muscle model. In a Na-free medium flux of [1-14C]creatine was reduced (p < 0.001), however the addition of various uraemic toxins, insulin, parathyroid hormone and the alteration of pH had no effect on creatine influx. The variance of red cell creatine levels in uraemic patients was significantly different from controls (p < 0.02) and the plasma to red cell creatine gradient was low in some patients.